As is known, group transmissions consist of two or more transmission groups usually arranged in series, the combination of which can produce a large number of gears. Increasingly, they are designed as semi-automatic change-speed transmissions, for example consisting of an input transmission or splitter group, a main transmission and a downstream or range group. Such transmissions are used especially in utility vehicles since they provide a particularly fine gradation of gears, for example with 12 or 16 gears, and they work with high efficiency. For a smaller number of gears, configurations having only a main transmission and a splitter group or a main transmission and a range group are also possible. Furthermore, compared with manually shifted transmissions they are very comfortable to use, and compared with conventional automatic transmissions they are particularly economical to manufacture and operate.
As a result of their structure, conventional multi-group transmissions, like all manual or semi-automatic transmissions that are not shifted under load, are characterized by a traction force interruption during gearshifts since the force flow from the drive motor is always interrupted by disengaging a clutch so that the engaged gear can be disengaged while free from load, the transmission and the drive motor can be synchronized to a connection rotational speed while in a neutral position, and the target gear can then be engaged. This results in restricted driving performance due to a loss of speed, and sometimes in higher fuel consumption. Whereas in passenger cars the slight loss of driving dynamics caused by this traction force interruption is usually perceived as no more than annoying, for example in the case of a sporty driving style, with heavy utility vehicles driving uphill, the speed can decrease to a point where an upshift to a desired target gear becomes impossible and undesired downshifts, crawl driving or even additional starting processes are required.
To help out in such situations, solutions have already been proposed which reduce or completely avoid these traction force interruptions. From DE 10 2006 024 370 A1 by the present applicant such a semi-automatic multi-group transmission is known, which comprises a splitter group as the input transmission, a main transmission and a range group as the output group or downstream transmission. The design of this known multi-group transmission with the splitter group and the main transmission enables a direct gear to be engaged as an intermediate gear during a gearshift. For this, a temporary connection is formed by means of a powershift clutch between an input shaft of the input transmission and a main shaft of the main transmission. This relieves the load on the main transmission and the splitter group so that the engaged gear can be disengaged, the transmission synchronized and the target gear engaged, while the starting clutch remains coupled. During this the powershift clutch transmits a motor torque to the transmission output so that a dynamical torque that becomes free during a rotational speed drop between the original and target gears is largely used to compensate the traction force interruption.
The powershift clutch of the multi-group transmission described in DE 10 2006 024 370 A1, which is a friction clutch, can be arranged between the input transmission or splitter group and the main transmission, or between the frictional starting clutch and the splitter group. In any case the starting clutch and the powershift clutch are made and arranged separately, and each is actuated by a respective associated control device.
Another multi-group transmission is known from DE 10 2005 046 894 A1 by the present applicant. This transmission comprises a main group and a range group downstream from it. A drive motor can be connected by means of a frictional starting or motor clutch to the motor-side end of a transmission input shaft. In turn, the transmission input shaft can be connected to an output shaft of the transmission by means of a frictional powershift clutch arranged within the range transmission. The other end of the transmission input shaft is connected to an input side of the powershift clutch, and an output shaft of the main transmission is coupled to an output side of the powershift clutch.
The range transmission is of planetary design, such that the output shaft is connected to a planetary carrier and the output side of the powershift clutch can be coupled, via a sun gear and a planetary gearset carried by the planetary carrier, to the output shaft. In this way a traction force interruption during a shifting process of the main transmission can be avoided. To avoid a traction force interruption during a range shift in the range group, the output side of the powershift clutch can also be connected directly to the planetary carrier and hence to the output shaft. In this way the traction force can also be supported during shifting processes involving a range shift. In this multi-group transmission as well, the starting clutch and the powershift clutch are arranged separately and are in the form of friction clutches.
Finally, from the not previously published German patent application DE 10 2008 001 200 a multi-group transmission of a motor vehicle is known, in which means are provided for engaging an intermediate gear in order to reduce or avoid traction force interruptions during gearshifts. This group transmission comprises an input or splitter group with two gear constants, a main transmission with three further gear-ratio gearsets and a range group made as a planetary transmission. Parallel to a transmission input shaft are arranged two countershafts on which the fixed gearwheels of the gear-ratio gearsets are fixed. Between the two ratio gearsets of the gear constants of the splitter group, between the ratio gearset of the second gear constant and the first ratio gearset of the main transmission and between the two further ratio gearsets of the main transmission there is arranged in each case a respective synchronized shifting device that acts on both sides, by means of which loose gearwheels of the gearsets can be connected to associated transmission shafts in a rotationally fixed manner.
For this group transmission to be designed as simply and compactly as possible and to be simple to control and comfortable and energy-saving in use, between a drive motor and a transmission input there is arranged a dual clutch device comprising two friction clutches, one of these clutches being actuated as a starting element to connect a driveshaft of the drive motor to a transmission input shaft and the other clutch being actuated as a powershift element to engage an intermediate gear by connecting the driveshaft of the drive motor to a main shaft of the transmission which extends at least partially through the transmission.